The proposed studies form part of a continuing investigation into the cellular mechanisms underlying the transport of water, ions, and water soluble nonelectrolytes across the epithelial cell layer of the small intestine. Specifically, the project seeks to focus on the kinetics, metabolic dependence, and electrophysiological correlates of ionic movements across this tissue. Coupling between ionic transfer processes (e.g. sodium and chloride transport) and between the absorption of ions (particularly sodium ions) and that of non-electrolytes such as sugars and neutral amino acids, and the effects of such coupling on the electrophysiology of small intestinal epithelium is of major concern within the overall scope of the investigation. Experimental procedures include measurements of the following parameters: transepithelial potential difference and short circuit current, membrane potentials of epithelial cells, intracellular ionic activities (using ion-selective electrodes) and transepthelial fluxes (using radiotracers). Because of its exceptional in vitro stability and its close functional resemblance to mammalian small intestine, the isolated small intestine of the bullfrog is used as an experimental preparation. The goal of this investigation is to provide information which, it is hoped, will help to form a basis for the development of new conceptual and technical approaches to the management and control of human disorders which stem from intestinal malfunction. In addition, the techniques employed and the results obtained in this study will, hopefully, contribute significantly to the broader problems of epithelial physiology and pathophysiology. BIBLIOGRAPHIC REFERENCES: Armstrong, W. McD. Wojtkowski, W., and Bixenman, W. R. A new solid-state microelectrode for measuring intracellular chloride activities. Biochem. Biophys. Acta 465:165-170 (1977). Myers, C.J., and W. McD. Armstrong. Electrophysiology of Epithelial Cell Layers - A finite difference model. Biophys. J. 17, 21a (1977) (Abstract).